Electric starter motor with holder for permanent magnets

ABSTRACT

An electric machine, particularly for starting devices, is suggested. Permanent magnets (4 to 9) with assigned flux conducting pieces (10 to 15) are arranged in the housing (1) of the electric machine. The permanent magnets (4 to 9), together with the flux conducting pieces (10 to 15), are preassembled in two rings (18, 19) as retaining parts to form a constructional unit. Each ring (18, 19) has a cylindrical portion (20; 30) which contacts the end portions of the inner side (21; 22) of the permanent magnets (4 to 9) or the flux conducting pieces (10 to 15). A flangelike edge (25; 33) of the rings (18; 19) contacts the front sides (23, 24; 31, 32) of the permanent magnets (4 to 9) and the flux conducting pieces (10 to 15). Tabs (26, 27; 34, 35), which contact the end portions of the free longitudinal sides (17; 28 ) of the permanent magnets (4 to 9) or the flux conducting pieces (10 to 15), are bent out from the edges 25 and 33. A ring (19) is provided with fastening means (36 to 41) for the detachable fastening of the magnet group (4 to 15, 18, 19) at projections (3) of the housing (1).

PRIOR ART

The invention is based on an electric machine, particularly for startingdevices of internal combustion engines, which includes a cylindricalhousing and, within the housing a plurality of arcuate permanent magnetseach having a convex side in contact with the inner wall of the housing,an opposite concave side, two opposite longitudinal sides and frontsides, and a plurality of magnetic flux conducting pieces arranged,respectively, in contact with a longitudinal side of assigned permanentmagnets. An electric machine in which the permanent magnets are held ina housing by means of retaining springs is already known. The retainingsprings are arranged between two adjacent permanent magnets in eachinstance and have resilliently contacting spring arms as well asfastening means at one front face of the permanent magnets in order tohold the permanent magnets in the correct position in the housing. Bymeans of the deliberately produced dome effect, no additional fasteningof the permanent magnets in the housing are required in this knownarrangement. If in a known electric machine the permanent magnets areprovided with magnetic flux conducting pieces, then radial forces act onthe flux conducting pieces in the direction toward the armature, whichradial forces are so great that the retaining springs must beadditionally fastened in the housing with at least one rivet in order tohold the permanent magnets and flux conducting pieces in fixed positionin the housing. Such a fastening of the permanent magnets with theassigned flux conducting pieces has the disadvantage that it requiresnumerous fastening parts in the form of retaining springs and rivetsand, when taken with high assembly costs, is no longer economical.

SUMMARY OF THE INVENTION

The object of the invention is to provide an electric machine of thetype named in the beginning in which the permanent magnets, togetherwith the flux conducting pieces, can be securely, but detachably,arranged and fastened in the housing at low cost with simple means.

In keeping with this object and others which will become apparenthereafter, one feature of this invention resides in the provision ofresilient retaining means for fastening the permanent magnets andconducting pieces in fixed, circumferential and longitudinal positionsin the housing, the retaining means consisting of two facing rings eachhaving a flangelike edge part matching the inner diameter of the housingand engaging assigned front sides of the permanent magnets andconducting pieces, a cylindrical part projecting at right angles fromthe edge part to contact assigned end portions of the concave sides ofthe permanent magnets and the conducting pieces, the edge parts beingprovided with retaining projections for engaging end portions of freelongitudinal sides of respective permanent magnets and conducting piecesand the edge part of at least one of the rings being provided withaxially directed projections for detacheably fastening the one ring tothe inner wall of the housing. Preferably, at least one catch projectionis formed on the inner wall of the housing, and at least one axiallydirected projection of the one ring can snap engage at the catchprojection. At the other ring, there is provided at least one resilientprojection, which is bent outwardly over the edge part of the other ringto engage an intermediate bearing or drive bearing arranged at an endside of the housing.

It is advantageous that only two retaining rings, which can be usedregardless of the respective magnet length and clockwise orcounterclockwise rotation of the electric machine, are required in orderto securely hold the permanent magnets with the assigned flux conductingpieces. Moreover, the retaining rings make it possible to fix thepermanent magnets and flux conducting pieces in a form-locking mannerand to preassemble the magnet group. Moreover, the retaining rings forma mechanical protection for the magnets when.

Advantageous developments of the electric machine indicated in the mainclaim are made possible by means of It is particularly advantageous thatretaining projections, fastening projections and means which compensatefor tolerances are formed on one retaining ring, by means of whichretaining parts a ring can catch at projections of the housing so as tobe detachable, while the other ring comprises resilient projections forcompensating the relatively considerable manufacturing tolerances in thelongitudinal direction. In addition, the annular retaining parts can beformed, according to the type and load of the electric machine, fromspring steel, a viscoplastic, heat-resistant plastic or light metal.

DRAWING

An embodiment example of the invention is shown in the drawing and isexplained in more detail in the following description.

FIG. 1 shows the housing of an electric machine in longitudinal section,

FIG. 2 shows a front view in the direction of arrow II and

FIG. 3 shows a front view in the direction of arrow III in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Radially projecting catch projections 3 are constructed by means ofstamping, for example, at the inner wall 2 of a cylindrical housing 1 ofan electric machine so as to be perpendicular to the longitudinal axisof the housing 1. A magnet group is detachably inserted in thehousing 1. The magnet group is formed from three permanent magnet pairs,wherein a magnetic flux conducting piece 10 to 15 is assigned to eachpermanent magnet 4 to 9. The permanent magnets 4 to 9 are curved in sucha way that their outer convex side is adapted to the inner wall 2 of thehousing 1. According to the direction of rotation of the armature of theelectric machine, which armature is known per se and is not shown inmore detail, each flux conducting piece 10 to 15 contacts one or theother longitudinal side 16 or 17 of the assigned permanent magnet 4 to9.

The permanent magnets 4 to 9, together with the flux conducting pieces10 to 15, are preassembled as magnet groups by means of resilientretaining means. The retaining means consist of two rings 18 and 19made, for example, of spring steel. According to the type and load, therings can also be formed as formed parts made of viscoplastic syntheticmaterial or light metal, such as aluminum.

The ring 18 has an axially directed cylindrical portion 20 on which anend end portions of the concave sides 21 or 22 of the permanent magnets4 to 9, or the flux conducting pieces 10 to 15, rest, the edge portionadjoining a front side 23 and 24 of the permanent magnet 4 to 9 or theflux conducting piece 10 to 15.

The ring 18 has a flangelike edge part 25 which extends perpendicularlyrelative to the cylindrical portion 20 to engage the front side 23 or 24of the permanent magnets 5 to 9 and the flux conducting pieces 10 to 15.The diameter of the edge part 25, matches the inner diameter of thehousing. Tabs 26 and 27 are punched out of the edge part 25 and are bentto engage the free longitudinal side 17 of respective permanent magnets4 to 9 and a free longitudinal side 28 of the flux conducting pieces 10to 15 adjoining the assigned permanent magnets 4 to 9. The permanentmagnets 4 to 9, together with the flux conducting pieces 10 to 15, arefixed in their positions relative to one another in the longitudinal andcircumferential direction by means of the edge part 25 and the tabs 26and 27. Moreover, the flux conducting pieces 10 to 15 are held at therespective assigned permanent magnets 4 to 9 in a form-locking manner bymeans of the tabs 26, 27.

In addition, six spring arms 29 are bent out of the edge part 29, toproject outwardly away from the front sides 23 and 24. Their manner ofoperation is explained further on.

The ring 19 likewise has a cylindrical portion 30. The latter supportsan end portion of the concave side 21 and 22 of the permanent magnets 4to 9 and the flux conducting pieces 10 to 15.

The ring 19 likewise has a flangelike edge part 33. Tabs 34 and 35 arealso punched out of the edge part 33 and bent at the longitudinal side17 of the permanent magnets 4 to 9 and at the longitudinal side 28 ofthe flux conducting pieces 10 to 15. Accordingly, the permanent magnets4 to 9, with the adjoining flux conducting pieces 10 to 15, are alignedrelative to one another and held in their longitudinal, circumferentialand radial directions as a magnet group and preassembled as aconstructional unit by means of the rings 18 and 19. Moreover, the rings18, 19 form a mechanical protection when inserting the magnet group inthe housing 1, particularly for the front side areas of the magnet group4 to 15.

Four fastening tabs 36 to 39 are punched out at the edge part 33 of thering 19 in addition and are bent away at right angles relative to theedge part 33, but in the opposite direction of the tabs 34, 35. A springtongue 40 comprising a slot 41 is constructed in each fastening tab 36to 39.

The preassembled magnet group 4 to 15, 18, 19 is pushed into the housing1 until the fastening tabs 36 to 39 catch with their slotted springtongues 40 at the catch projections 3 which project radially at theinner wall 2 of the housing 1. The magnet group 4 to 15, 18, 19 isaccordingly fastened in the housing 1 so as to be fixed in its positionand so as to be detachable. The housing 1 is covered opposite the frontsides 23 and 24 magnets and conducting pieces and opposite the edge part25 of the ring 18 by an intermediate bearing 42 at which the spring arms29 of the ring 18 are supported. The intermediate bearing 42 serves, ina manner known per se and not shown in more detail, as a bearing for thearmature shaft of the electric machine, the armature shaft also beingknown per se and not shown in more detail. The intermediate bearing 42is provided with spring tongues 43 at the circumference, which springtongues 43 are arranged and fastened between the front sides of thehousing 1 and a drive bearing 44 in a manner known per se. In general,the drive bearing 44 and a commutator bearing, not shown, which isarranged at the front side 45 of the housing 1, are fastened at thehousing 1 by means of tie rods 46. Through-openings are provided for thetie rods 46 projecting through the magnet group 4 to 15, 18, 19 by meansof correspondingly bending away the tab pairs 26, 27 in the edge 25 ofthe ring 18, as well as tab pairs 34, 35 in the edge 33 of the ring 19.The tab pairs 26, 27; 34, 35 serve, in turn, as mechanical protectionfor the permanent magnets 4 to 9, together with conducting pieces 10 to15, when inserting the tie rods 46.

In known constructions with intermediate bearings the drive bearing isarranged directly at the housing 1 and the spring arms 29 are thensupported at the drive bearing.

We claim:
 1. In an electric machine, of the type having a cylindricalhousing and within the housing, a plurality of arcuate permanent magnetseach having a convex side contact with the inner wall of the housing, anopposite concave side, two opposite longitudinal sides and front sides,and a plurality of magnetic flux conducting pieces arranged,respectively, in contact with a longitudinal side of assigned permanentmagnets, the improvement comprising resilient retaining means forfastening said permanent magnets and conducting pieces in fixedcircumferential and longitudinal positions in the housing, saidretaining means consisting of two facing rings each having a flangelikeedge part matching the inner diameter of said housing and engagingassigned front sides of said permanent magnets and conducting pieces, acylindrical part projecting at right angles from said edge part tocontact assigned end portions of the concave sides of the permanentmagnets and the conducting pieces, said edge parts including retainingprojections for engaging end portions of free longitudinal sides ofrespective permanent magnets and conducting pieces and the edge part ofat least one of said rings being provided with axially directedprojections for detacheably fastening said one ring to the inner wall ofthe housing.
 2. The retaining means according to claim 1, wherein atleast one catch projection is formed on the inner wall of the housing toengage at least one of said axially directed projection of said onering, and the other ring having at least one resilient projection, whichis bent outwardly over the edge part of the other ring to engage anintermediate bearing or drive bearing arranged at an end side of thehousing.
 3. The retaining means according to claim 1, wherein the ringsconsist of spring steel.
 4. The retaining means according to claim 1,wherein the rings are constructed as formed parts of viscoplasticmaterial.
 5. The retaining means according to claim 1, wherein the ringsare constructed as injection molded parts of light metal.